The item is in accordance with standards of VDE 0664, CEE27 and BS 4293 etc., applying to the circuit of AC 50/60Hz, 240V single phase, 415V three phases and below it for industrial and mining enterprise, building trade, commerce and family. To mainly prevent electric fire and personal casualty accident caused by personal electric shock or leakage of electrified wire netting, this ELCB is a current-operated, fast leakage protector of pure electromagnetic type, which can break off fault circuit rapidly in order to avoid occurrence of accident. The item is precise in structure, less elements, without auxiliary power and high working reliability The function of the switch won’t be influenced by ambient temperature and lightning. The mutual inductor of the item is used to test vector differential value of passing current, and produces a relevant output power and add it to the tripper in secondary winding , if the current of vector differential value of protected circuit of personal electric shock is up to or over leakage operating current, the tripper will at and cut off so as that the item will take effect of protection.